In recent years, there is a need for an image-forming apparatus that enables resources to be further saved, and duplex printing is frequently performed on sheets such as a blank form, an OHP sheet, a plastic sheet, and cloth. Accordingly, it is important for an image-forming apparatus that has a duplex printing function to increase the number of sheets on which duplex printing can be performed per unit time, that is, to have an improved productivity of duplex printing.
PTL 1 discloses the related art in which a reversing portion at which a sheet is reversed includes a reverse roller group that includes a drive roller that rotates in only one direction when the drive roller is subjected to a driving force, a first driven roller, and a second driven roller. The first driven roller, the drive roller, and the second driven roller of the reverse roller group are arranged in this order in a substantially straight line in a direction that intersects a direction in which the sheet is conveyed. The first driven roller faces the drive roller and forms a first nip portion. The second driven roller faces the drive roller, is on the opposite side of the drive roller from the first driven roller, and forms a second nip portion.
In PTL 1, at the reversing portion, the sheet is reversed in the following manner. An image is formed on a first surface of the sheet, and the sheet is conveyed toward the first nip portion of the reverse roller group. Subsequently, at the first nip portion, the sheet is conveyed in a first direction in which the sheet is discharged from the reverse roller group. A trailing end of the sheet in the direction in which the sheet is conveyed passes through the first nip portion. The reversing portion includes a switch back portion that temporarily receives the sheet on the downstream side of the first nip portion in the direction in which the sheet is conveyed. The sheet that passes through the first nip portion is received by the switch back portion. Subsequently, the sheet that is temporarily received by the switch back portion falls due to the weight of the sheet, and the trailing end of the sheet is guided to the second nip portion of the reverse roller group. Since the drive roller rotates in only one direction, the sheet that is nipped at the second nip portion is conveyed in a second direction opposite the first direction in which the sheet is conveyed at the first nip portion. Subsequently, the sheet is conveyed to an image-forming unit again, and an image is formed on a second surface of the sheet. Subsequently, the sheet is conveyed to a sheet-discharging unit that is disposed at a position that differs from that of the reversing portion. The sheet discharged from the image-forming apparatus by using a discharge roller of the sheet-discharging unit.
In PTL 1, the sheet is completely discharged from the reverse roller group to the switch back portion, the sheet is temporarily received by the switch back portion, and the nip portion at which the sheet is nipped is switched from the first nip portion to the second nip portion. In the case where duplex printing is continuously performed on sheets with this structure, while a first sheet that has passed through the first nip portion is received by the switch back portion, a subsequent second sheet can be conveyed to the first nip portion.
However, with the structure in PTL 1, in which the sheets are completely discharged from the first nip portion of the reverse roller group to reverse the sheets, it is necessary for the switch back portion that temporarily receives the sheets to be disposed on the downstream side of the reverse roller group in the direction in which the sheet is conveyed. In this case, since the sheet that is discharged from the reverse roller group is received by the switch back portion, it is necessary for the image-forming apparatus to include the sheet-discharging unit that discharges the sheet from the image-forming apparatus at the position that differs from that of the reversing portion that reverses the sheet. This makes a problem of an increase in the size of the image-forming apparatus.